1. Field of the Invention (Technical Field)
The present invention relates to a two-stage membrane-based apparatus and method for production of gas from biological materials using fermentative and photosynthetic processes.
2. Description of Related Art
Note that the following discussion refers to a number of publications by author(s) and year of publication, and that due to recent publication dates certain publications are not to be considered as prior art vis-à-vis the present invention. Discussion of such publications herein is given for more complete background and is not to be construed as an admission that such publications are prior art for patentability determination purposes.
Hydrogen (H2) has been identified as a renewable and pollution-free high-efficiency carrier that has the potential to replace the nonrenewable fossil fuels of today. However, currently available H2 production technologies, such as electrolysis or biomass gasification, are energy-intensive and expensive. Many technical challenges relating to hydrogen's generation, storage, and usage remain to be solved before it can be widely adapted for use.
Hydrogen can be produced by thermochemical, electrochemical, or biological processes. Of the three, biological processes are emerging as more environment-friendly, less energy-intensive, and sustainable. Recent research suggests that hydrogen produced via biological processes or from biomass, i.e. biohydrogen, is feasible, where the biomass is organic matter such as chemical feedstock or waste streams, and can be sustainable and cost-effective in the latter case. Current research has identified three processes as viable for biohydrogen production: biophotolysis by cyanobateria; photofermentation by anoxygenic phototrophic bacteria; and fermentation by anaerobic bacteria. The following are examples of such hydrogen production technologies.
U.S. Pat. No. 7,083,956 to Paterek, entitled “Method For Hydrogen Production From Organic Wastes Using a Two-Phase Bioreactor System”, issued Aug. 1, 2006, discloses a method for hydrogen production from organic wastes and manures using a two-phase bioreactor system with biodegradable solid being introduced into first stage anaerobic bioreactor utilizing indigenous microflora. The liquid effluent, including fatty acids, is transferred into second stage anaerobic bioreactor, which is not photofermentative. Hydrogen passes through semi-permeable fibers of the second stage.
U.S. Pat. No. 6,887,692 to Paterek, entitled “Method and Apparatus For Hydrogen Production From Organic Wastes and Manure,” issued May, 2005, discloses a method and system for hydrogen production in which a feedstock of at least one biodegradable solid is introduced into a first stage anaerobic bioreactor and a liquid effluent formed. A hollow fiber membrane separates liquid phases. The liquid effluent is transferred into a second stage anaerobic bioreactor having a plurality of hollow semipermeable fibers having an outer surface coated with a biofilm formed by at least one hydrogenogenic bacteria, which forms hydrogen gas within the lumen of the hollow semipermeable fibers. The hydrogen thus produced is removed from the lumen of the hollow semipermeable fibers.
U.S. Pat. No. 7,138,046 to Roychowdhury, entitled “Process For Production Of Hydrogen From Anaerobically Decomposed Organic Materials,” issued Nov. 21, 2006, discloses a process for the production of hydrogen from anaerobically decomposed organic materials by applying an electric potential to anaerobically decomposed organic materials to form hydrogen gas.
Anaerobic technology has been proven to be energy-efficient in stabilizing organic waste streams. Reports from several laboratory studies and full-scale projects have documented successful applications of this technology in stabilizing liquid waste streams and generating energy in the form of gaseous methane. However, large-scale application of this technology in stabilizing particulate wastes to produce energy has been hindered by the poor kinetics of the overall process. Conversion of particulate organic wastes to gaseous methane involves multiple steps in series and parallel, diverse groups of microorganisms, and different environments.
The following have been recognized as important stages in the process. In the first stage, acidogenic organisms solubilize particulate substrates extracellularly by enzymatic hydrolysis. In the second stage, acidogenic organisms catabolize the products of the first stage into volatile organic acids, carbon dioxide, and hydrogen. In the next stage, acetogenic organisms convert the products of the second stage to acetic acid. Finally, methanogenic organisms convert the acetic acid to carbon dioxide and methane.
Hydrogen is removed by absorption in materials such as Pd and LaNi5; stripping by boiling or by a recirculating gas such as nitrogen; or evaporation at large surface areas. However, these approaches are expensive, energy-intensive, or impractical for large-scale applications.
Typical gas components in biogas include CH4, N2, CO2, H2O (vapor) and trace amounts of NH3, H2S, and HCl. Traditional biogas separation processes focus on CH4 enrichment, which is similar to CO2 separation from natural gas. Both adsorption and membrane processes have previously been applied in biogas separation. A hollow fiber membrane separation process for natural gas upgrade has been commercialized by Air Liquide (MEDAL-Air Liquid). Palladium and alloy membranes for H2 separation from gas mixtures have been extensively studied and documented. The mechanism of H2 transport through such membranes involves the following series of steps: adsorption; dissociation; ionization; diffusion; reassociation; and desorption. Within the metal, H2 loses its electron to the palladium structure and diffuses through the membrane as a proton. At the exit surface the reverse process occurs. The trace components including NH3, H2S, and HCl in biogas could potentially poison the precious metal components in the H2 separation membrane and significantly reduce the membrane performance and stability. Microporous SiO2 membranes have shown high selectivity and permeability for H2 at close to ambient temperature.
While recent research has reported on biohydrogen production from liquid organic substrates in pure and sterile forms, embodiments of the present invention preferably comprise an apparatus and method to produce hydrogen from solid biological material, such as organic solid wastes (OSWs) or the like. Unlike the inventions mentioned above, embodiments of the present invention preferably comprise an apparatus and method of anaerobic hydrolysis and fermentation, or a chemical conversion of carbohydrates into alcohols or acids in the absence of oxygen, in tandem with photofermentation, and comprising a gas-specific membrane. Embodiments of the present invention preferably comprise a single vessel design incorporating at least two steps, an anaerobic fermentation stage and a photofermentation stage, and preferably comprise a membrane, preferably a hollow fiber membrane, separating fluid or gaseous phases. Other embodiments of the present invention preferably comprise an apparatus and method comprising biological conversion of acids to a gas and a heat treatment to suppress methanogens.
Embodiments of the present invention preferably comprise a two-step process configuration for hydrogen production, preferably at room temperature, from biomaterials with the first step preferably comprising generating H2 gas or other gases through anaerobic hydrolysis and fermentation and the second step comprising generating additional H2 gas or other gases through photofermentation of the products of the first stage and stabilizing the waste.
For sustainable H2 production, substrates should preferably be carbohydrates from renewable sources at sufficient concentrations requiring minimum pretreatment, and available throughout the year at low cost. Materials comprising OSWs meet these requirements, and may be ideal feedstocks for biohydrogen production from the standpoint of pollution prevention, economics, and sustainability. Cellulose, hemicellulose, and lignin are the primary components of plant cells, and are thus the primary components of OSWs such as biomass wastes, food wastes, and farm wastes. The conversion of cellulose and hemicellulose first to glucose and xylose, respectively, and then to hydrogen, therefore, is a rational and sustainable solution to abatement of pollution, depletion of fossil fuel reserves, and emissions of greenhouse gases.
Biohydrogen has recently been produced from liquid organic substrates in pure and sterile forms, but there is a need for producing biohydrogen from any kind of biomaterials, including solid biomaterials. Additionally, combining waste stabilization and H2 production in this manner conserves limited resources and be a cost-effective and sustainable approach. Cattle manure is currently produced at a rate of 2.2×104 kg/yr/cow, which translates to a COD equivalent of 2×1014 kg/yr. The current practice of applying the manure to the ground as a fertilizer runs in the face of new regulations that prohibit land application.
There is currently a need for an optimal process configuration for development of a dry digestion process, modifying anaerobic technology to produce hydrogen rather than methane. While methane generation from wastes is well understood and has been reported upon, embodiments of the present invention preferably generate gas by two processes in tandem, which has previously not been accomplished. Even though the viability of the two processes has been demonstrated individually, the present invention integrates the two for larger scale practical applications.